Experimental validation of a steady periodic analytical model for Breathing Walls

摘要

The Breathing Wall behaviour under variable boundary conditions is described by an analytical model based on a one-dimensional porous domain crossed by air and subject to third type steady periodic boundary conditions. To the best of the authors' knowledge, its experimental validation is not provided in literature. In this work, a new model is derived considering Dirichlet steady periodic boundary conditions. The model is experimentally validated testing a 1 m2 no-fines concrete sample in the Dual Air Vented Thermal Box apparatus, specially improved to replicate dynamic thermal conditions. The experiments show that increasing the air flow velocity across the Breathing Wall from 0 to 12 mm/s enhances thermal coupling between the two environments, namely reduces the wall thermal capacity, with a decrease in the penetration time from 4.3 h to 3 h. The model shows a very good agreement with experimental data when predicting temperature distribution across the domain, with error averages and standard deviations within the thermocouple accuracy after calibration, assumed to be 0.15 degrees C. The lesser yet good agreement concerning conduction heat flux density is explained in terms of accuracy in the measurement of the boundary conditions and critical issues in the heat flow measure itself (i.e. probe thermal resistance, thermal contact, emissivity mismatch).